Filters of the type used for filtering particulate matter from engine intake air sometimes include one or more layers of a porous filter material that is formed into a convoluted pattern, often referred to in the industry as fluted filter media.
In one commonly utilized form of a filter element, the filter element defines a longitudinal axis in first and second axial ends of the filter element, with the filter element including a central core, and a length of fluted filter media wound about the central core, with the flutes of the media oriented substantially longitudinal, thereby providing filtration for a flow of fluid passing axially through the filter element. Such filter elements are typically installed within a housing, or duct, in such a manner that the filter element can periodically be removed for cleaning or replacement with a fresh filter element. A seal between the filter element and the housing is typically provided, in such a manner that none of the fluid flowing through the housing can bypass the filter element, thereby ensuring all fluid passing through the housing enter one axial end of the filter element and exit from the opposite axial end of the filter element.
Where possible, filter elements of the type described above are typically formed into a circular cylindrical shape, with the filter media being wound about a round central core. In some applications, however, it is necessary to form filter elements into non-cylindrical shapes, to fit space constraints of the particular application. For example, in a racetrack shaped element, the cross sectional shape of the filter element is racetrack shaped, having a pair of curved semi-circular ends joined by a pair of straight segments. In such racetrack shaped filter elements, and in filter elements having other non-circular cross sectional shapes, such as oval or rectangular, for example, the length of fluted filter material is wound about a non-circular central core. Such non-circular central cores may have cross sections that are substantially rectangular in shape.
One prior approach to provide a racetrack shaped filter element was disclosed in U.S. Pat. Nos. 7,001,450; 6,746,518 and 6,547,857 to Gieseke et al., wherein a fluted filter media is coiled about a rectangular shaped center board. As is well known in the art, and stated in the patent to Gieseke et al., fluted filter media typically exhibits an inherent shape memory which can cause the media to bow outwardly, radially, away from the center board. In a filter element having a cylindrical central core, this inherent curvature memory is typically not problematic, in that the curvature of the media will not interfere with, and may actually assist in, pulling the media down onto the core, or onto a previously wound layer of the media.
Another prior approach to forming a racetrack shaped filter element is shown in U.S. Pat. Nos. 7,008,467 and 6,966,940 to Krisko et al. Krisko et al. uses a core construction including a racetrack shaped non-cylindrical wall member having opposing walls defining an open volume within the non-cylindrical member. In cross section, the non-cylindrical member has the appearance, generally, of a flattened cylindrical shaped tube having flat opposing side walls joined at opposite ends by curved walls, surrounding the open volume. The core construction of Krisko et al. further includes structural moldings and plugs located within the open volume, for providing strength, and axially closing off the open volume to ensure that fluid cannot leak through the open volume inside of the non-cylindrical member.
The center core construction of Krisko et al. is even more complex than the center board of Gieseke et al. as described above. The core construction of Krisko et al. also appears to include a substantial volume of axis material, making such a core construction undesirably expensive to produce and heavier then necessary. The core construction of Krisko et al. can result in a significant amount of extra material which must be disposed of or incinerated when the filter element is replaced.
Because the central core is essentially a non-operating part of the completed filter, it is desirable that the central core be fabricated at minimum cost, utilizing as little material as possible, and having a configuration which can be readily manufactured in a form that is also readily disposable or incinerable. It is also desirable, in some applications, that the central core be fabricated in a manner which is as light in weight as possible.
It is desirable, therefore, to provide an improved method and apparatus for manufacturing a fluid filter element having a non-cylindrical elongated shape such as a racetrack shape, in a manner which overcomes one or more of the problems discussed above, and/or provide improved utility over the prior art.